Composite materials, such as graphite-epoxy, are used in the manufacture of aircraft structures because they have high strength-to-weight ratios. Initially, only lightly loaded or non-critical parts were manufactured from composite materials. As the technology has advanced, however, a greater percentage of aircraft parts, including critical structural members, have been manufactured using composite materials.
FIG. 1 illustrates a prior art joining apparatus 100 for joining a sandwich panel 102 to a structure 104. The joining apparatus 100 includes a base 106 having a flange 108 projecting outwardly from a foot 110. The sandwich panel 102 has a maximum thickness 112 and converges to a minimum thickness 114 at a connection portion 116. The sandwich panel 102 includes a low density core portion 118 situated between skin portions 120. The core portion 118 includes a wedge portion 122 where the skin portions converge to form the connection portion 116. The flange 108 and the connection portion 116 are coupled with a fastener 124.
As shown in FIG. 1, the connection portion 116 is provided for a number of reasons. One reason is to isolate the core portion 118 with the skin portions 120. As discussed, the core portion 118 is formed from a low density material and therefore is not ideal for receiving the fastener 124. Another reason is to increase the strength of the sandwich panel 102 at the connection portion 116. The connection portion 116 includes increased skin thickness as compared to the thickness of the skin portion 120 adjacent to the core portion 118.
There are a number of shortcomings to the joining apparatus 100 described above. For example, the wedge portion 122 and corresponding structure (e.g., converging skin portions 120) increase part complexity and typically requires a special manufacturing process and specific design requirements for each different application. This makes modifications difficult when design requirements are not satisfied and increases design and manufacturing costs. In addition, manufacturing processes for securing coupling may be reduced or eliminated by improved methods for fastening the sandwich panel 102 and the base 106. The fastener 124 also adds additional weight to the joining apparatus 100, which is disadvantageous in aircraft applications or other applications where weight reduction is beneficial.